A thrust bearing of a type noted above is usually employed in a submersible pump or a submersible motor, etc. One type of such thrust bearing utilizing dynamic pressure in liquid is known as a thrust bearing comprising a spiral element. For example, such spiral element is disclosed in Japanese Patent Publication No. 12121/66 and U.S. patent application Ser. No. 627,731 filed on July 3, 1984 assigned to the same assignee as this application. The thrust bearing having such a spiral element as described above is required to be rotated in one direction only to produce the dynamic pressure between the spiral element and an opposing element which are caused to move in relative rotation. This type of bearing has been satisfactory for its intended use; however, should there be any mistake such as erroneous connection of wires leading to the power source, the bearing would be subjected to rotation in the wrong direction so that no dynamic pressure is produced between the elements. Therefore, under such situation, if the shaft already has a thrust load imposed on it, seizure may be caused in the bearing.
If it is intended to allow the rotation of the shaft in both the normal and opposite directions, another type of thrust bearing, e.g. a tilting pad type metal bearing, must be used. However, such metal bearing is rather easily abraded compared to the thrust bearing using a spiral element or is subject to troubles caused by foreign materials entrained on the bearing surfaces, is associated with a relatively large mechanical loss consuming a large amount of power and needs a lubricating medium of relatively high viscosity. Also, such conventional metal bearing is not suitable for equipment adapted to handle liquid of high temperature. Therefore, it has been desired to have a thrust bearing which can overcome the drawbacks noted above.